In a case of different departments or sales regions, you may want to keep all of your data separate so the data is getting mixed up. To do this, you would use a combination of user groups and privacy settings.
I'll use an example of 2 sales teams, one in Illinois and the other in Colorado.
You first need to create your User Groups. This guide will show you how to create the user groups.
Create all of the groups you need, and then you need to make data private. You can do this as you are importing or if everything is already in the system, you can bulk update the permissions. This guide will show you how to make data private. When you make something private, make sure you use the dropdown menu and select the group.
As long as the team are just users, they will not see the data for the other groups.